Etching of high aspect ration structures

ABSTRACT

Plasma etching processes using a plasma containing fluorine as well as bromine and/or iodine are suited for high aspect ratio etching of trenches, contact holes or other apertures in silicon oxide materials. The plasma is produced using at least one fluorine-containing source gas and at least one bromine- or iodine-containing source gas. Bromine/iodine components of the plasma protect the aperture sidewalls from lateral attack by free fluorine, thus advantageously reducing a tendency for bowing of the sidewalls. Ion bombardment suppresses absorption of bromine/iodine components on the etch front, thus facilitating advancement of the etch front without significantly impacting taper.

STATEMENT OF RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/894,460 (allowed), filed Jun. 28, 2001 and titled “ETCHING OF HIGHASPECT RATIO STRUCTURES,” which is commonly assigned and incorporated byreference in its entirety herein.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to methods of forming aperturesin a dielectric layer and, more particularly, to methods of controllingprofile in high aspect ratio contact apertures formed in silicon oxidematerials.

BACKGROUND OF THE INVENTION

To meet demands for faster processors and higher capacity memories,integrated circuit (IC) designers are focusing on decreasing the minimumfeature size within integrated circuits. By minimizing the feature sizewithin an integrated circuit, device density on an individual chipincreases exponentially, as desired, enabling designers to meet thedemands imposed on them. One such feature is the so-called contactaperture, or “contact,” which is typically a circular hole extendingthrough a layer of dielectric material to a structure formed on or in anunderlying semiconductor substrate.

As circuit component structures, including contacts, enter the sub-halfmicron range of dimensions, tolerances become more critical and demandmore precise process parameters. For example, sub-half micron contactsmust hold the top contact diameter (top CD) within a narrow toleranceband while a high aspect ratio contact is etched through a dielectriclayer, and the contact itself must exhibit a substantially cylindricalcross section (i.e., little taper) to achieve an effective contact areawith the underlying substrate. As used herein, the term “high aspectratio” as applied to contact structures is currently contemplated toindicate a depth to width, or diameter, ratio of about five to one ormore (≧5:1). In addition to contacts, it is also necessary in someinstances to etch high aspect ratio sub-half micron width lines ortrenches through dielectric layers, and fabrication of these structuresdemands similar precision. Mixtures of these structures, i.e., holes andtrenches, are common in semiconductor fabrication, particularly in thoseusing dual-damascene techniques.

It is highly desirable to etch high aspect ratio contacts through alayer of doped silicon dioxide such as borophosphosilicate glass, orBPSG, and sometimes through additional layers such as other oxides,silicon nitride or inorganic, dielectric anti-reflective coating (DARC)films between the mask and the substrate silicon. Desired contactstructures to be achieved would have a minimum nominal depth of 1–2 μm,an aspect ratio of approximately 5:1 to 10:1 or higher, and a profileangle of greater than approximately 87° as measured from a horizontalplane of the substrate. High selectivity for BPSG to the substratesilicon is preferred, as is the ability to etch the other films, such asthe aforementioned silicon nitride and DARC films.

For the reasons stated above, and for other reasons stated below thatwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art foralternative methods for producing high aspect ratio structures.

SUMMARY

Embodiments described herein utilize a plasma etching process with aplasma containing fluorine, as well as bromine and/or iodine for etchinghigh aspect ratio trenches, contact holes or other apertures in siliconoxide materials. The plasma is produced using at least onefluorine-containing source gas, such as a perfluorocarbon orhydrofluorocarbon gas, and at least one bromine- or iodine-containingsource gas, such as hydrogen bromide, hydrogen iodide, a bromine- oriodine-substituted fluorocarbon or a bromine- or iodine-substitutedhydrofluorocarbon. Bromine/iodine components of the plasma protect theaperture sidewalls from lateral attack by free fluorine, thusadvantageously reducing a tendency for bowing of the sidewalls. Ionbombardment suppresses absorption of bromine/iodine components on theetch front, thus facilitating advancement of the etch front withoutsignificantly impacting taper. Such methods are particularlyadvantageous in forming very high aspect ratios of 8:1 or higher.

For one embodiment, the invention provides a method of forming anaperture in a silicon oxide layer. The method includes generating aplasma containing fluorine and bromine and/or iodine, accelerating ionsfrom the plasma toward a surface of the silicon oxide layer, and etchingan exposed portion of the silicon oxide layer, thereby advancing an etchfront into the silicon oxide layer and forming the aperture havingsidewalls. The method further includes absorbing or depositing bromineand/or iodine components on the sidewalls of the aperture and continuingto advance the etch front and absorb bromine and/or iodine components onthe sidewalls of the aperture until a desired aspect ratio is attained.The bromine and/or iodine content is sufficient to produce a taper angleof the sidewalls of greater than about 87°.

For another embodiment, the invention provides a method of forming anaperture in a silicon oxide layer. The method includes generating aplasma containing fluorine and bromine, accelerating ions from theplasma toward a surface of the silicon oxide layer, and etching anexposed portion of the silicon oxide layer, thereby exposing sidewallsof the silicon oxide layer. The method further includes absorbing ordepositing components containing bromine on the sidewalls of the siliconoxide layer and continuing to etch the exposed portion of the siliconoxide layer and to absorb or deposit components containing bromine onthe sidewalls of the silicon oxide layer until an aperture having adesired aspect ratio is attained. A content of the bromine in the plasmais sufficient to produce a taper angle of the sidewalls of greater thanabout 87°.

For yet another embodiment, the invention provides a method of formingan aperture in a silicon oxide layer. The method includes generating aplasma containing fluorine and iodine, accelerating ions from the plasmatoward a surface of the silicon oxide layer, and etching an exposedportion of the silicon oxide layer, thereby exposing sidewalls of thesilicon oxide layer. The method further includes absorbing or depositingcomponents containing iodine on the sidewalls of the silicon oxide layerand continuing to etch the exposed portion of the silicon oxide layerand to absorb or deposit components containing iodine on the sidewallsof the silicon oxide layer until an aperture having a desired aspectratio is attained. A content of the iodine in the plasma is sufficientto produce a taper angle of the sidewalls of greater than about 87°.

For a further embodiment, the invention provides a method of forming anaperture in a silicon oxide layer. The method includes generating aplasma comprising at least one first source gas and at least one secondsource gas. Each first source gas is a fluorocarbon gas and each secondsource gas is either a bromine-containing gas or an iodine-containinggas. The method further includes accelerating ions from the plasmaperpendicularly toward a surface of the silicon oxide layer andadvancing an etch front in the silicon oxide layer, thereby exposingsidewalls of the silicon oxide layer. The method still further includesabsorbing or depositing components from the plasma on the sidewalls ofthe silicon oxide layer, wherein the absorbed or deposited componentsmay be bromine-containing components and/or iodine-containingcomponents. The absorbed or deposited components are sufficient topassivate the sidewalls of the silicon oxide layer from attack byfluorine-containing components of the plasma. The method still furtherincludes continuing to advance the etch front until a desired aspectratio is attained, wherein the desired aspect ratio is greater thanabout 8:1.

For a still further embodiment, the invention provides a method offorming an aperture in a silicon oxide layer. The method includesgenerating a plasma comprising at least one first source gas and atleast one second source gas, wherein each first source gas is afluorocarbon gas and each second source gas is a bromine-containing gasand/or an iodine-containing gas. The method further includesaccelerating ions from the plasma perpendicularly toward a surface ofthe silicon oxide layer and advancing an etch front in the silicon oxidelayer, thereby exposing sidewalls of the silicon oxide layer. The methodstill further includes forming a polymer residue on the sidewalls of thesilicon oxide layer and brominating and/or iodizing the polymer residueon the sidewalls of the silicon oxide layer, thereby passivating thepolymer residue from attack by fluorine-containing components of theplasma. The method still further includes continuing to advance the etchfront until a desired aspect ratio is attained, wherein the desiredaspect ratio is greater than about 5:1.

Further embodiments of the invention include methods of varying scope.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a portion of an integrated circuitdevice showing formation of an aperture in a silicon oxide layer in atypical fluoride etch process.

FIGS. 2A–2B are cross-sectional views of a portion of an integratedcircuit device showing formation of an aperture in a silicon oxide layerin accordance with embodiments of the invention.

DETAILED DESCRIPTION

In the following detailed description of the present embodiments,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration specific embodiments inwhich the invention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood-that other embodiments may beutilized and that process, electrical or mechanical changes may be madewithout departing from the scope of the present invention. The termswafer or substrate used in the following description include any basesemiconductor structure. Examples include silicon-on-sapphire (SOS)technology, silicon-on-insulator (SOI) technology, thin film transistor(TFT) technology, doped and undoped semiconductors, epitaxial layers ofa silicon supported by a base semiconductor structure, as well as othersemiconductor structures well known to one skilled in the art.Furthermore, when reference is made to a wafer or substrate in thefollowing description, previous process steps may have been utilized toform regions/junctions in the base semiconductor structure, and theterms wafer and substrate include the underlying layers containing suchregions/junctions. The following detailed description is, therefore, notto be taken in a limiting sense, and the scope of the present inventionis defined only by the appended claims and equivalents thereof.

Embodiments described herein utilize a plasma etching process with aplasma containing fluorine as well as bromine and/or iodine for etchinghigh aspect ratio trenches, contact holes or other apertures in siliconoxide materials. The plasma is produced using at least onefluorine-containing source gas, such as a perfluorocarbon orhydrofluorocarbon gas, and at least one bromine- or iodine-containingsource gas, such as hydrogen bromide, hydrogen iodide, a bromine- oriodine-substituted fluorocarbon or a bromine- or iodine-substitutedhydrofluorocarbon. Bromine/iodine components of the plasma protect theaperture sidewalls from lateral attack by free fluorine, thusadvantageously reducing a tendency for bowing of the sidewalls.

Various embodiments further utilize ion bombardment during the etchingprocess. Ions accelerated at and impinging upon the etch front will tendto dislodge bromine/iodine components absorbed or deposited on the etchfront, thus allowing free fluorine and fluorine-containing ions toadvance the etch front. By facilitating advancement of the etch frontwhile reducing lateral attack, the resulting aperture can be formed withimproved profile at aspect ratios of 5:1, 8:1, 10:1 and higher, and withtop widths of less than 0.3 μm.

FIG. 1 is a cross-sectional view of a portion of an integrated circuitdevice 100 showing formation of an aperture 150 in a silicon oxide layer105 in a typical fluoride etch process. The silicon oxide layer 105 maybe a doped or undoped silicon oxide material. Some examples includesilicon dioxide (SiO₂), tetraethylorthosilicate (TEOS), siliconoxynitrides (SiO_(x)N_(y)), borosilicate glass (BSG), phosphosilicateglass (PSG) and borophosphosilicate glass (BPSG).

A mask 110 is formed and patterned on the silicon oxide layer 105 in amanner well known in the art, e.g., by standard photolithographictechniques. Ions 115 are generated in a plasma etch process and directedtoward the surface 135 of the integrated circuit device 100. Examples ofequipment and techniques for plasma etching are described in U.S. Pat.No. 6,123,862 issued Sep. 26, 2000 to Donohoe et al., which is commonlyassigned. In general, a plasma is formed over the surface 135 of thedevice 100 and a bias power is supplied to the substrate containing thedevice 100, or to a support or chuck supporting the substrate, toaccelerate the ions 115 toward the surface 135. The fluorine-ionsimpinging on the exposed silicon oxide layer 105 advance the etch front130. During etching, a polymer residue (not shown in FIG. 1) may form onthe sidewalls of the aperture 150. This polymer residue is oftenpurposefully formed in order to minimize bowing, but such polymerresidue also can detrimentally impact taper.

The processing described with reference to FIG. 1 can produce anacceptable taper, measured as angle θ relative to a plane horizontal tothe surface 135, at lower aspect ratios. Taper angles are preferablygreater than about 87° and preferably no greater than approximately 90°.More acute angles, i.e., angles less than 87°, cause detrimentalreductions in aperture width or diameter while less acute angles, i.e.,angles greater than 90°, cause detrimental reentrant profiles. Reducingtaper angles is referred to as increasing taper while increasing taperangles is referred to as decreasing taper.

As an example of the effect of taper angle, at an 87° taper angle, thebottom of a contact hole theoretically will be approximately 60% of itstop diameter at an aspect ratio of 8:1 or a loss of diameter ofapproximately 40%. At an 85° taper angle, the loss of diameter will bein excess of approximately 70% at an aspect ratio of 8:1; the aspectratio would have to be reduced to less than 5:1 to maintain of diameterloss of around 40% or less. And at an 82° taper angle, an aspect ratioof 8:1 cannot theoretically be reached as the bottom diameter will pinchshut; the aspect ratio would have to be reduced to around 3:1 tomaintain a diameter loss of around 40% or less. Accordingly, maintainingdesirable taper becomes increasingly important as the desired aspectratio, and the resulting etch depth, increases.

To maintain desirable taper as the aspect ratio increases, etchconditions generally must be altered, such as increasing the fluorinecontent of the etchant or increasing the energy of the ions 115. Theseetch conditions used to maintain taper at higher aspect ratios willdetrimentally lead to increased levels of free fluorine 120 and aresulting propensity for bowing 125. Bowing 125 is generally formed bythe reaction of free fluorine 120 on sidewalls of the aperture 150.Because the free fluorine 120 is a neutral, it cannot be acceleratedperpendicularly toward the surface 135 as with the ions 115. The freefluorine 120 will thus tend to “bounce” into the aperture 150 and tendto accumulate toward the top of the aperture 150. The accumulated freefluorine 120 laterally etches the sidewalls producing the characteristicbowing 125. High-density source gases, e.g., high-order fluorocarbons,are preferred for generation of the plasma. However, such high-densitysource gases also have a tendency to produce higher levels of freefluorine.

FIG. 2A is a cross-sectional view of a portion of an integrated circuitdevice 200 showing formation of an aperture 250 in a silicon oxide layer205 in an etch process in accordance with an embodiment of theinvention. The silicon oxide layer 205 may be a doped or undoped siliconoxide material. Some examples include silicon dioxide (SiO₂),tetraethylorthosilicate (TEOS), silicon oxynitrides (SiO_(x)N_(y)),borosilicate glass (BSG), phosphosilicate glass (PSG) andborophosphosilicate glass (BPSG).

A mask 210 is formed and patterned on the silicon oxide layer 205 in amanner well known in the art, e.g., by standard photolithographictechniques. Ions 215 are generated in a plasma etch process and directedtoward the surface 235 of the integrated circuit device 200 as wasdescribed with reference to FIG. 1. Ions 215 generated in the plasma areaccelerated toward the surface 235. Ions 215 impinging on exposedportions of the silicon oxide layer 205 advance the etch front 230.

The plasma is generated using at least one fluorine-containing sourcegas and at least one bromine- or iodine-containing source gas. For oneembodiment, the composition of the plasma is modified during the etchprocess such that the bromine- or iodine-containing source gas is notadded to the plasma until the etch front 230 advances into the siliconoxide layer 205. The fluorine-containing source gases are fluorocarbongases including perfluorocarbon or hydrofluorocarbon gases. Someexamples include CHF₃ (trifluoromethane), CH₂F₂ (difluoromethane), C₂HF₅(pentafluoroethane), C₃F₆ (perfluoropropene), C₃F₈ (perfluoropropane)and C₄F₈ (perfluorobutene), as well as higher order perfluorocarbons andother hydrofluorocarbons. Some examples of bromine- or iodine-containingsource gases include HBr (hydrogen bromide), HI (hydrogen iodide), CF₃Br(bromotrifluoromethane) and CF₃I (iodotrifluoromethane), as well asadditional bromine- or iodine-substituted fluorocarbons or bromine- oriodine-substituted hydrofluorocarbons. For one embodiment, thefluorine-containing source gas contains difluoromethane. For a furtherembodiment, the plasma is generated using difluoromethane and hydrogenbromide.

Neutral bromine (or iodine) components from the plasma preferentiallyabsorb or deposit on sidewalls of the aperture without attacking exposedsurfaces of the silicon oxide layer 205. The absorbed or depositedcomponents may contain free bromine, free iodine or other neutralcomponents containing bromine or iodine. If the sidewalls of theaperture 250 contain a polymer residue 240 (as shown in FIG. 2B), thebromine (or iodine) components may brominate (or iodize) the polymer,thus passivating the polymer residue 240. If the polymer residue 240 isexposed to the halogen-containing components during formation, thepolymer residue 240 may incorporate such halogen-containing componentswithin the polymer layer itself as additional polymer residue is formedoverlying the absorbed components. For one embodiment, the compositionof the plasma is modified during the etch process such that the bromine-or iodine-containing source gas is not added to the plasma until atleast a portion of the polymer residue 240 is formed. For anotherembodiment, the composition of the plasma is modified during the etchprocess such that the bromine- or iodine-containing source gas is notadded to the plasma until after the polymer residue 240 is formed.

The bromine (or iodine) components sterically hinder any free fluorine220 from attacking the sidewalls of the aperture 250, with or without apolymer residue 240, thus reducing any tendency to create bowing. Inaddition, as the energy of absorption of the bromine (or iodine)components is low relative to the energy of the incoming ions 215, theabsorption of bromine (or iodine) components will tend to be lessened atthe etch front 230 as the incoming ions 215 will suppress accumulationof these components at the etch front; because the incoming ions 215 areaccelerated predominantly perpendicularly to the surface 235, bromine(or iodine) components absorbed to the sidewalls will remain relativelyundisturbed by the incoming ions 215. The absorption of brominecomponents is preferred over the absorption of iodine components as theiodine components will be more difficult to dislodge from the etch front230 and may thus have a tendency to increase taper relative to bromine.

To suppress accumulation of the bromine (or iodine) compounds on theetch front 230 and to provide desirable etch rates, the power suppliedto the plasma etching process must be sufficiently high. For plasmaetching equipment of the type such as an IPS system available fromApplied Materials, Santa Clara, Calif., USA, source power to the chamberis preferably maintained between about 1000 and 2000 watts, and morepreferably at about 1500 watts. Bias power to the device 200 or itssupport is preferably maintained at less than about 1500 watts andgreater than about 800 watts, and most preferably greater than about 900watts. Such power levels are appropriate for etching apertures in 200 mmsubstrates. Power levels must be scaled, in a manner well known in theart, for larger or smaller substrates.

Processing pressure is generally maintained above approximately 5 mTorr,preferably between about 30 and 60 mTorr, and more preferably at about45 mTorr. As a general matter, with an increase of pressure in thechamber, the power must also increase to prevent excessive taper in theprofile of the aperture.

The source gases are typically delivered to an etch chamber at a totalflow rate of preferably between approximately 20 and 80 sccm, and morepreferably between approximately 40 and 50 sccm. An inert gas, e.g.,helium or argon, may also be delivered to the etch chamber at a flowrate of approximately 0 to 100 sccm, and preferably betweenapproximately 40 and 50 sccm.

The bromine/iodine content of the source gases is an amount sufficientto produce bromine/iodine neutrals capable of passivating the aperturesidewalls, thus protecting the sidewalls from detrimental attack by freefluorine. This amount is dependent upon the source gases chosen togenerate the plasma, the temperature/pressure/powers chosen for theplasma etch process, and the aspect ratio of the aperture being formed.The atomic ratio of bromine and/or iodine to fluorine in the sourcegases is deemed sufficient when a taper angle of greater than or equalto approximately 87° is maintained in the aperture for the givenprocessing conditions. For one embodiment, the bromine/iodine content ofthe source gases is modified during the etch process as the aspect ratioincreases. For a further embodiment, the bromine/iodine content of thesource gases is reduced during the etch process as the aspect ratioincreases.

Those skilled in the art will recognize that specific values for processconditions are dependent upon the type of etch equipment or tool chosenfor the task. Appropriate process conditions must be determined for thechosen tool. One way to determine appropriate process conditions is tochoose initial process conditions that produce a desired taper, butunacceptable bowing. The process is then performed using the initialprocess conditions, but adding bromine- and/or iodine-containingcomponents in the process gas flows at a point in the process preferablyprior to the formation of bowing. The addition of bromine- and/oriodine-containing components may occur at the beginning of the process,during formation of a polymer residue, or after formation of the polymerresidue. The effect of the bromine and/or iodine addition is thendetermined and the initial process conditions are modified to producethe desired taper. The modifications to the initial process conditionsare suggested to be those modifications that compensate for the effectof the bromine and/or iodine addition. For example, if the additionproduces a reduction in taper angle, the preferred modification would bea modification suggested by the tool to increase taper angle. Suchmodifications could include changes in power, pressure, process gasflows, backside inert gas pressure, etc. This process may be reiterateduntil a profile having a desired taper and bowing is achieved.

The foregoing figures were used to aid the understanding of theaccompanying text. However, the figures are not drawn to scale andrelative sizing of individual features and layers are not necessarilyindicative of the relative dimensions of such individual features orlayers in application. Accordingly, the drawings are not to be used fordimensional characterization.

CONCLUSION

Embodiments described herein utilize a plasma etching process with aplasma containing fluorine as well as bromine and/or iodine for etchinghigh aspect ratio trenches, contact holes or other apertures in siliconoxide materials. The plasma is produced using at least onefluorine-containing source gas and at least one bromine- oriodine-containing source gas. Bromine/iodine components of the plasmaprotect the aperture sidewalls from lateral attack by free fluorine,thus advantageously reducing a tendency for bowing of the sidewalls. Ionbombardment suppresses absorption or deposit of bromine/iodinecomponents on the etch front, thus facilitating advancement of the etchfront without significantly impacting taper. Apertures formed inaccordance with the various embodiments may be used, for example, assupport structures for the formation of container capacitors and ascontact holes and trenches in the fabrication of integrated circuitdevices such as memory devices.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement that is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. Many adaptations ofthe invention will be apparent to those of ordinary skill in the art.Accordingly, this application is intended to cover any adaptations orvariations of the invention. It is manifestly intended that thisinvention be limited only by the following claims and equivalentsthereof.

1. A method of forming an aperture in a silicon oxide layer, the methodcomprising: generating a plasma containing fluorine, wherein the plasmais substantially devoid of bromine or iodine; accelerating ions from theplasma toward a surface of the silicon oxide layer; etching an exposedportion of the silicon oxide layer, thereby advancing an etch front intothe silicon oxide layer and forming the aperture having sidewalls; afteradvancing the etch front into the silicon oxide layer, adding at leastone element selected from the group consisting of bromine and iodine tothe plasma; and continuing to advance the etch front after adding the atleast one element.
 2. The method of claim 1, wherein accelerating ionsfrom the plasma toward a surface of the silicon oxide layer furthercomprises accelerating ions from the plasma toward a surface of thesilicon oxide layer using a bias power of at least approximately 900watts.
 3. The method of claim 1, wherein generating a plasma containingfluorine further comprises generating a plasma having at least onefluorine-containing source gas.
 4. The method of claim 3, wherein eachfluorine-containing source gas is selected from the group consisting ofperfluorocarbons and hydrofluorocarbons.
 5. The method of claim 4,wherein each fluorine-containing source gas is selected from the groupconsisting of trifluoromethane, difluoromethane, pentafluoroethane,perfluoropropene, perfluoropropane and perfluorobutene.
 6. The method ofclaim 1, wherein adding at least one element selected from the groupconsisting of bromine and iodine to the plasma further comprises addinga source gas selected from the group consisting of hydrogen bromide,bromotrifluoromethane, a bromine-substituted fluorocarbon, abromine-substituted hydrofluorocarbon, hydrogen iodide,iodotrifluoromethane, an iodine-substituted fluorocarbon and aniodine-substituted hydrofluorocarbon.
 7. The method of claim 1, whereinthe silicon oxide layer contains a silicon oxide material selected fromthe group consisting of doped and undoped silicon oxide materials. 8.The method of claim 7, wherein the silicon oxide layer contains asilicon oxide material selected from the group consisting of silicondioxide, tetraethylorthosilicate, a silicon oxynitride, borosilicateglass, phosphosilicate glass and borophosphosilicate glass.
 9. A methodof forming an aperture in a silicon oxide layer, the method comprising:generating a plasma containing at least one fluorine-containing sourcegas selected from the group consisting of perfluorocarbons andhydrofluorocarbons, wherein the plasma is substantially devoid ofbromine or iodine; accelerating ions from the plasma toward a surface ofthe silicon oxide layer; etching an exposed portion of the silicon oxidelayer, thereby advancing an etch front into the silicon oxide layer andforming the aperture having sidewalls; after advancing the etch frontinto the silicon oxide layer, adding at least one additional source gasselected from the group consisting of hydrogen bromide,bromotrifluoromethane, a bromine-substituted fluorocarbon, abromine-substituted hydrofluorocarbon, hydrogen iodide,iodotrifluoromethane, an iodine-substituted fluorocarbon and aniodine-substituted hydrofluorocarbon to the plasma; and continuing toadvance the etch front after adding the at least one additional sourcegas.
 10. The method of claim 9, wherein each fluorine-containing sourcegas is selected from the group consisting of trifluoromethane,difluoromethane, pentafluoroethane, perfluoropropene, perfluoropropaneand perfluorobutene.
 11. The method of claim 9, wherein the siliconoxide layer contains a silicon oxide material selected from the groupconsisting of doped and undoped silicon oxide materials.
 12. A method offorming an aperture in a silicon oxide layer, the method comprising:generating a first plasma comprising a fluorine-containing source gasand an inert gas; accelerating ions from the first plasma toward asurface of the silicon oxide layer; etching an exposed portion of thesilicon oxide layer, thereby exposing sidewalls of the silicon oxidelayer; after exposing sidewalls of the silicon oxide layer, generating asecond plasma comprising a fluorine-containing source gas, an inert gasand a source gas comprising at least one element selected from the groupconsisting of bromine and iodine, wherein the source gas comprising atleast one element selected from the group consisting of bromine andiodine is not a component of the first plasma; accelerating ions fromthe second plasma toward a surface of the silicon oxide layer; andcontinuing to etch the exposed portion of the silicon oxide layer untilan aperture having a desired aspect ratio is attained.
 13. The method ofclaim 12, wherein each fluorine-containing source gas is selected fromthe group consisting of perfluorocarbons and hydrofluorocarbons.
 14. Themethod of claim 12, wherein the source gas comprising at least oneelement selected from the group consisting of bromine and iodine isselected from the group consisting of hydrogen bromide,bromotrifluoromethane, a bromine-substituted fluorocarbon, abromine-substituted hydrofluorocarbon, hydrogen iodide,iodotrifluoromethane, an iodine-substituted fluorocarbon and aniodine-substituted hydrofluorocarbon.
 15. The method of claim 12,wherein the silicon oxide layer contains a silicon oxide materialselected from the group consisting of doped and undoped silicon oxidematerials.
 16. A method of forming an aperture in a silicon oxide layer,the method comprising: generating a first plasma comprising an inert gasand a fluorine-containing source gas selected from the group consistingof perfluorocarbons and hydrofluorocarbons; accelerating ions from thefirst plasma toward a surface of the silicon oxide layer; etching anexposed portion of the silicon oxide layer, thereby exposing sidewallsof the silicon oxide layer; after exposing sidewalls of the siliconoxide layer, generating a second plasma comprising an inert gas, afluorine-containing source gas, and at least one additional source gasthat is not a component of the first plasma, wherein each additionalsource gas is selected from the group consisting of hydrogen bromide,bromotrifluoromethane, a bromine-substituted fluorocarbon, abromine-substituted hydrofluorocarbon, hydrogen iodide,iodotrifluoromethane, an iodine-substituted fluorocarbon and aniodine-substituted hydrofluorocarbon; accelerating ions from the secondplasma toward a surface of the silicon oxide layer; and continuing toetch the exposed portion of the silicon oxide layer until an aperturehaving a desired aspect ratio is attained.
 17. The method of claim 16,wherein the silicon oxide layer contains a silicon oxide materialselected from the group consisting of doped and undoped silicon oxidematerials.
 18. A method of forming an aperture in a silicon oxide layer,the method comprising: generating a first plasma consisting essentiallyof a fluorine-containing source gas and an inert gas; accelerating ionsfrom the first plasma toward a surface of the silicon oxide layer;etching an exposed portion of the silicon oxide layer, thereby exposingsidewalls of the silicon oxide layer; after exposing sidewalls of thesilicon oxide layer, generating a second plasma consisting essentiallyof a fluorine-containing source gas, a bromine-containing source gas andan inert gas; accelerating ions from the second plasma toward a surfaceof the silicon oxide layer; and continuing to etch the exposed portionof the silicon oxide layer until an aperture having a desired aspectratio is attained.
 19. A method of forming an aperture in a siliconoxide layer, the method comprising: generating a first plasma consistingessentially of a fluorine-containing source gas and an inert gas;accelerating ions from the first plasma toward a surface of the siliconoxide layer; etching an exposed portion of the silicon oxide layer,thereby exposing sidewalls of the silicon oxide layer; after exposingsidewalls of the silicon oxide layer, generating a second plasmaconsisting essentially of a fluorine-containing source gas, aiodine-containing source gas and an inert gas; accelerating ions fromthe second plasma toward a surface of the silicon oxide layer; andcontinuing to etch the exposed portion of the silicon oxide layer untilan aperture having a desired aspect ratio is attained.